AuthorTopic: Failing MSAN Ports (Read 1708 times)

would the knowledgeable people on this forum mind taking a look at my connection statistics and let me know if you have any theories.

I'll leave all the voltage & wiring talk to others. But just based on what I see from the graph.. it looks indicative of EMI/RFI or faulty line card.Years ago there were a whole batch of faulty BTw line cards. I can't recall which MSAN type they were on now, but Azzaka would recall - and BTw ended up swapping them all out. TT use Huawei MSANs .. but I don't think it was Huawei that BTw had the problem with.

However the symptoms when graphed, showed something like what yours is doing. It took them a while to track it down because at first the natural assumption was EMI type REIN. It was Zen who put forward a suggestion that it may be line card due to them having had several more techie uses who were graphing using DSLstats and routerstats... and Azzaka who worked for Zen at that time put 2+2 together which is why he knew so much about it.

The reason I mention it... if it is a faulty line card then swapping you to another port may not be the cure as depending which line card is in use by TT, from memory they could have up to 96 ports :/

This is an interesting thought. I think we can rule out EMI/RFI here too as this would not result in the symptoms disappearing when the port is changed, nor is this compatible with the DSL dropping when the phone is picked up.

The symptoms disappearing for a few months after a port change is also problematic for the theory regarding a bad line card, though perhaps one could have a situation where all the ports on a card are in some way 'weak' and will fail after a few months use. Ideally to check this I'd record stats against some other line on this line card, naturally though I'm not going to be able to find out who else is connected to it. I do have a relative who has a TT ADSL service provisioned from the same exchange, though their connection is fine and has been for years.

Today I borrowed a Keysight U1232A True RMS multimeter and did some more investigation.

Firstly, the steady 110V reading from the M-830B should be disregarded. Measuring a 12V battery with this multimeter on the AC ranges results in a reading of 27V, so the 110V reading is likely just an artefact of the 50V DC on the line.

The Keysight multimeter reports much lower AC voltages: initially about 30V falling to 0.1V within a couple of seconds. On the low impedance setting a steady 0V is seen.

The Amprobe multimeter still gives the wildly fluctuating reading from 20 to 200V on auto range mode. However when set to any range manually, only 0.1V is seen.

Other than steadily working through all the available ports, I can't think of any obvious way to test for a faulty line-card.

From what I recall, they don't all fail at the same time which is what made it harder to find. I don't have all the details as it was Azzaka who was speaking to Openreach about it... and its several years ago now. All I do know is that when the fault presents it looked remarkably REIN like on Routerstats/DSLstats. Unfortunately Azzaka no longer works at Zen so isnt around to ask.

It is something to bear in mind that if a line is displaying unattributable REIN like symptoms, then the port could be faulty.Please bear in mind I may be giving you a red herring by mentioning a faulty line card, but with you having had port swaps which have also gone bad it does sound a bit suspect.

I wonder if you can get a Lift and Shift to another Line card (not port) on the MSAN. I wouldn't even know how to approach TT with that, as I think port swaps are usually initiated by the Openreach engineer suspecting a bad port. Problem is with you being with TT, unlike with BTw then the request goes back to the SP.

I would think the best course of action would be explaining to the Openreach engineer that you are now on your 4th port which fails after a certain period... and if he thinks it could be the line card rather than port.

From what I recall, they don't all fail at the same time which is what made it harder to find. I don't have all the details as it was Azzaka who was speaking to Openreach about it... and its several years ago now. All I do know is that when the fault presents it looked remarkably REIN like on Routerstats/DSLstats. Unfortunately Azzaka no longer works at Zen so isnt around to ask.

Ah, understood. This makes it more likely that this could be the issue here too. Sorry for doubting this earlier, I was somewhat blinded by the supposed discovery of the alien AC voltage!

I wonder if you can get a Lift and Shift to another Line card (not port) on the MSAN. I wouldn't even know how to approach TT with that, as I think port swaps are usually initiated by the Openreach engineer suspecting a bad port. Problem is with you being with TT, unlike with BTw then the request goes back to the SP.

I would think the best course of action would be explaining to the Openreach engineer that you are now on your 4th port which fails after a certain period... and if he thinks it could be the line card rather than port.

Unfortunately my experience of TT's customer service is that it is impossible to have a technical discussion of that nature. The previous port swaps have indeed been initiated by the Openreach engineers. I'll definitely suggest a Lift and Shift to a different line card to the engineer and see where we go from there.

In any case, I will make the engineer aware of the previous port failures and provide the name of the SFI engineer that identified this as the problem. Not doing this leads to a high probability of a 'Right When Tested' visit since the PQ usually passes.

Thanks very much burakkucat and kitz for your invaluable advice. I'll update this thread as I go for the benefit of anyone else that might suffer something similar, though I won't be able to do anything for the next few weeks as work commitments mean I can't have a day off for an engineer visit.

Well I'm back with a somewhat late update and I'm more confused than ever.

Since the 24th September the fault has disappeared. No more disconnections, high numbers of CRCs, SNRM fluctuations or noise on the phone. The odd bit: I did nothing! I have had no Openreach visits. I did not even tell TalkTalk. Simply the last loss of sync was at 08:43 on 24/09/2018, after which the errors dropped to a far more reasonable level and the SNRM became arrow straight. After about a week TalkTalk's DLM removed the high target SNRM and set this back to 6dB and all was fine. I've now reapplied an SNRM tweak to 3db and my connection has been in sync for 5 days with only 1 or 2 errored seconds per day. As far as I can see, everything is back to normal.

However I am completely at a loss as to what the problem was. The ending of the SNRM fluctuations could suggest a REIN source that no longer exists, however this explanation is not consistent (unless someone more knowledgeable knows otherwise) with the problem being fixed previously by changing MSAN port. Nor is it consistent with the loss of sync on picking up the phone. The only thing I can think of is perhaps the line card got changed anyway due to someone else's problem / some other reason.

Perhaps we should wait for any input from Black Sheep, as he will have experienced all sorts of abnormal line/circuit conditions . . . possibly with alien AC voltages present.

My sincere apologies, gents ..... I've only just seen this ??

Regarding the AC Voltage that our hand-held testers will display during a PQT test ...... less than 1.0v is quite common, and even at 4.0v or under the PQT will still pass ..... and as mooted by you both, it is purely inductive from nearby power sources.